1. Field of the Invention
The present invention concerns an apparatus for perforating corrugated tubing. More particularly, the present invention concerns an apparatus for perforating corrugated tubing at a high rate of speed. Also, the present invention concerns a method for achieving the same.
2. Prior Art
Machines for perforating tubing are known. U.S. Pat. No. 3,824,886, issued Jul. 23, 1974 to Hegler, teaches an apparatus for cutting apertures in corrugated tubing by rotating the cutter circumferentially around the tubing. The cutter is disposed within a ridge on a wheel, which is driven by a transmission. The wheel and cutter cooperate with a roller to rotate about the tubing. The cutter travels in an epitrochoidal path around the outer surface of the tubing, causing a perforation where the cutter strikes the tubing. Hegler achieves perforations perpendicular to the axis of the tubing by this method.
While offering a relatively simple design to achieve its ends, Hegler is necessarily limited to perforating corrugated tubing at relatively low speeds due to the necessity of the wheel with cutter traveling the entire length of the corrugation. Increasing the traveling speed of the wheel beyond modest levels would result in miscuts in the tubing, such as cuts in the side walls of the corrugations instead of the valley thereof. Further, excessive wheel speed would cause the wheel to jump past corrugation, thus missing areas of the tubing and leaving these areas unperforated.
U.S. Pat. No. 4,180,357, issued Dec. 25, 1979 to Lupke et al., teaches an apparatus for perforating tubing. Lupke et al. teaches a machine having a plurality of lead screws for driving the tubing along an axial path, the lead screws having a meshing engagement with the corrugations of the tubing. Each lead screw is mounted on an axis of rotation parallel to the axial path of the tubing. Mounted upon each lead screw is a cutter, flanked on each side by a raised rib. The cutter is in a plane substantially at a right angle to the axial path and the cutter intermittently intersects the tubing. Lupke achieves rotation of the lead screws by a system of gear wheels coordinated such that pairs of lead screws cut the tubing simultaneously. Lupke can achieve a maximum horizontal tubing speed of 20 feet per minute while cutting. At speeds greater than 20 feet per minute, the apparatus of Lupke experiences difficulty in realigning the cutter and properly perforating the tubing.
U.S. Pat. No. 4,218,164, issued Aug. 19, 1980 to Lupke et al., teaches an improvement upon the previous Lupke apparatus. The plurality of lead screw members have mounted thereon a helically raised rib member centrally disposed thereon, the helical rib replacing the raised straight ribs of the previous apparatus. The cutter is disposed at the end of helical rib. The helical rib tends to facilitate entry of the cutter into the valley of the corrugation. The rib of the second Lupke apparatus extends around only a portion of the circumference of the shaft, thus continuing the teaching of intermittent intersection by the cutter as taught in the previous Lupke patent. The second Lupke apparatus achieves a horizontal tubing speed of approximately 40 to 50 feet per minute. At speeds in excess of 50 feet per minute, the second Lupke apparatus tends to climb the side walls of the corrugation and perforate either those walls or the crown of the corrugation.
Lupke et al. overcame the limitation of rotating the entire cutter wheel around the tubing as taught in Hegler. In the first Lupke apparatus the plurality of raised ribs essentially slowed the horizontal movement of the tubing long enough to effect the perforation. The second Lupke apparatus substituted the helical rib for the plurality of straight ribs. This alleviated the need to slow or stop the horizontal travel of the tubing along the axial path to effect the perforation, and works relatively well at lower speeds, i.e. speeds less than 50 feet per minute.
Both Lupke apparatuses encounter serious problems when greater speeds are attempted. When operated at speeds in excess of 50 feet per minute, the cutter in the first Lupke apparatus is not able to spring back to its original start position for the next intermittent engagement of the tubing. Thus, the cutter of Lupke is not able to perforate the valley of the corrugation, but rather cuts into the side wall, miscutting the tubing. Similar problems occur in the second Lupke apparatus.
Additionally, problems are encountered with the feed worms of Lupke. At high speeds, the vertical sides of the feed worms are unable to maintain their helical course in the corrugation. Thus, the worms tend to climb the side walls of the corrugations, crushing the crown of the tubing and skipping parts of the corrugation.
It is therefore the goal of the present invention to overcome the problems heretofore encountered in the prior art. It is a purpose of the present invention to provide an apparatus capable of perforating corrugated tubing at axial speeds in excess of 50 feet per minute, and further to perforate tubing at speeds of 150-200 feet per minute.
It is a further purpose of the present invention to achieve higher axial speeds while providing a simpler design by eliminating the necessity of complicated gear networks to achieve timing relationships.
It is a still further purpose of the present invention to provide an apparatus for perforating tubing of various diameters without the necessity of recalibrating timing relationships or the need for a completely new drive shaft arrangement.
It is to these ends that the present invention is directed.